Geologic Time Scale (Additional Reading) PDF

General Biology 2 Quarter 3 Lesson 2: Geologic Time Scale HISTORY OF LIFE ON EARTH THE GEOLOGIC TIME SCALE (GTS) → It is a time scale that divides Earth's geologic history into intervals of time defined by major events or changes on Earth. → It is a tabular repre...

General Biology 2 Quarter 3 Lesson 2: Geologic Time Scale HISTORY OF LIFE ON EARTH THE GEOLOGIC TIME SCALE (GTS) → It is a time scale that divides Earth's geologic history into intervals of time defined by major events or changes on Earth. → It is a tabular representation of the major divisions of the Earth's history. → A record of life forms and geologic events in Earth's history. NOTE: Age of the Earth is 4.6 billion years old, using Radiometric dating. MAJOR DIVISIONS OF GEOLOGIC TIME SCALE LONGEST TO SHORTEST TIME INTERVAL 1. EONS → The largest intervals of geologic time and are hundreds of millions of years in duration. 2. ERAS → Division that span time periods of ten to hundred million years. 3. PERIOD → Subdivided by Eras. A division of geologic history of no more than 100 million years. 4. EPOCHS → The smallest division in the Geologic Time Scale. Note: In the geologic time scale, "Ka" stands for "kilo annum" (thousands of years), "Ma" stands for "mega annum" (millions of years), and "Ga" stands for "giga annum" (billions of years) I. PRECAMBRIAN (HADEAN, ARCHEAN, PROTEROZOIC Eons) → Means "before Cambrian". → Includes 3 eons: Hadean, Archean Proterozoic. → Includes about 90% of all geologic time and spans the time from the beginning of the Earth about 4.6 billion years ago to 542 million years ago. → There were no major events. Only prokaryotic life is present and Earth was literally like hell. → Longest time in Earth's history. I- A. HADEAN EON → The Hadean Eon is the earliest eon, from 4.6 to 4 billion years ago. It is the least understood eon because there are no rocks from this time period that have been preserved on Earth. I-B. ARCHEAN EON → The Archean Eon is from 4 billion to 2.5 billion years ago this is the time when the Earth's crust began to solidify and the first life forms also appeared in Archean eon, but they were simple single-celled organisms. PROKARYOTES → First life form: common ancestor of all life; anaerobic. CYANOBACTERIA → Blue-green algae; First photosynthetic organism that thrived on Earth I-C. PROTEROZOIC EON → The Proterozoic Eon is from 2.5 billion to 541 million years ago. This is the time when the Earth's atmosphere and oceans became more oxygenated, and life became more complex. The first multicellular organisms appeared in the Proterozoic eon. PROTIST → The first eukaryotes II. PHANEROZOIC EON (PALEOZOIC ERA, MESOZOIC ERA, CENOZOIC Eras) II-A. PALEOZOIC ERA → Age of Ancient Life → An era of geologic time, from the end of the Precambrian to the beginning of the Mesozoic. → The word "paleozoic" is from Greek and means "old life" CAMBRIAN PERIOD (541 - 485.4 MILLION YEARS AGO) → There was an explosion of new kinds of organisms in the Cambrian (Cambrian explosion). → Small ocean invertebrates (animals without backbone) called trilobites, were very abundant. ORDOVICIAN PERIOD (485.4 - 443.8 MILLION YEARS) → The oceans were filled with invertebrates of many types. → The first fish evolved. → Plants colonized the land for the first time, but animals still remained in the water. SILURIAN PERIOD (443.8 - 419.2 MILLION YEARS AGO) → In the oceans, corals appeared and fish continued to evolve. → On the land, vascular plants appeared. With special tissue circulate waters and other materials, they could grow larger than earlier, nonvascular plants. DEVONIAN PERIOD (419.2 - 358.9 MILLION YEARS AGO) → The first seed plants evolved. Seed plants eventually became the most common type of land plants.  → Fish with lobe fins first evolved. They could breathe air when they raised their heads above water. Breathing would be necessary for animals to eventually colonize the land. → The first amphibians evolved to colonized the land, but they had to return to the water to reproduce. CARBONIFEROUS PERIOD (358.9 298.9 MILLION YEARS AGO) → Widespread forest left massive deposits of carbon that eventually turned to coal (great coal formation). → The first reptiles evolved. They were the first animals that could reproduce on dry land. TRANSITIONAL PERIOD PERMIAN PERIOD (298.9 - 251.9 MILLION YEARS AGO) → All the major land masses collided to form a super continent called Pangea. → Temperature was extreme, and the climate was dry. → Plants and animals evolved adaptations to dryness, such as waxy leaves or leathery skin to prevent water loss. → The Permian ended with a mass extinction. PERMIAN EXTINCTION → The era ended with the biggest mass extinction world had ever seen. This is known as the Permian extinction. II-B. MESOZOIC ERA → An era of geologic time between the Paleozoic and the Cenozoic. → "Middle Life"; started more than 280 million years ago. → "Age of Reptiles" TRIASSIC PERIOD (251 - 201 MILLION YEARS AGO) → The first dinosaurs branched off from reptiles and colonized the land, air, and water. → Huge seed ferns and conifers dominated the forest → The supercontinent Pangea started to separate into Laurasia and Gondwanaland. → Ended with mass extinction. JURASSIC PERIOD (201 - 145 MILLION YEARS AGO) → "The Golden Age of Dinosaurs"; earliest birds evolved from reptile ancestors. → All the major groups of mammals evolved, though individual mammals were still small size. → Flowering plants appeared for the first time and new insects also evolved to pollinate the flowers. → The continents continued to move apart, and volcanic activity was especially intense. CRETACEOUS PERIOD (145 - 66 MILLION YEARS AGO) → Dinosaurs reached their peak size and distribution. → Earth's overall climate was warm; even the poles lacked ice. → By the end of the Cretaceous, the continents were close to their present locations. → This period ended with the dramatic extinction of the dinosaurs. II-C. CENOZOIC ERA → from the Greek for “recent life,” → began 65.5 million years ago → divided into three periods: the Paleogene, Neogene, and Quaternary → Earth’s flora and fauna evolved toward those of the present. PALEOGENE PERIOD (65.5–23 MILLION YEARS AGO) → characterized by significant climate changes → diversification of various life forms, including mammals and marine organisms NEOGENE PERIOD (23–2.6 MILLION YEARS AGO) → started with the replacement of vast areas of forest by grasslands and savannahs → New food sources fostered further evolution of mammals and birds → Whales diversified in the seas, and sharks reached their largest size QUATERNARY PERIOD (2.6 MILLION YEARS AGO TO THE PRESENT) → famous for the many cycles of glacial growth and retreat, the extinction of many species of large mammals and birds, and the spread of humans. → divided into two epochs, from youngest to oldest: the Holocene and Pleistocene. → We are currently living in the Holocene epoch.